While it can sometimes feel like depression, you can have apathy without most of the classic signs of depression like sadness, early morning awakenings and loss of the experience of pleasure.
Most studies show that about a third of Parkinson's disease (PD) patients struggle with some degree of apathy. Apathy in PD most often co-occurs with depression and with cognitive deficits, like difficulty concentrating or calculating. But again, you can have apathy without either depression or cognitive dysfunction. No satisfactory treatment has yet been found for apathy in PD patients.